The present invention relates to a hybrid automotive vehicle, and more particularly to techniques for charging a battery by operating an electric generator while the vehicle is driven by an engine operated as a drive power source.
1. Field of the Invention
The present invention relates to a hybrid automotive vehicle, and more particularly to techniques for charting a battery by operating an electric generator while the vehicle is driven by an engine operated as a drive power source.
2. Discussion of Related Art
There is known a control apparatus for a hybrid automotive vehicle which includes, as drive power sources, an engine operable by combustion of a fuel and an electric motor. The control apparatus is adapted to charge a battery by operating an electric generator while the vehicle is driven by the engine operated as a drive power source. JP-A-9-98516 discloses an example of such a hybrid vehicle control apparatus, which is arranged to control an output of the engine so as to maximize the efficiency of charging of the battery in terms of the fuel economy, while taking into account of the energy conversion efficiency of the electric generator and the battery.
However, the above-indicated control apparatus arranged to control the output of the engine so as to maximize the efficiency of charging of the battery in terms of the fuel economy does not necessarily permit sufficiently high degrees of energy conversion efficiency and fuel economy, depending upon the vehicle drive force as desired by the vehicle operator and the amount by which the battery is charged. For instance, the amount of charging of the battery is determined by the amount of electric energy presently stored in the battery, and the electric generator is operated to generate the amount of electric energy corresponding to the determined amount of charging of the battery. In this case, the operating speed and drive torque of the electric generator decrease with a decrease in the amount of charging of the battery, so that the energy conversion efficiency decreases with a decrease in the amount of charging of the battery. On the other hand, the output of the engine is controlled so as to maximize the fuel economy. This arrangement may have a risk that the vehicle cannot be driven with a drive force which is as large as desired by the vehicle operator where the operator""s desired vehicle drive force is relatively large. The term xe2x80x9camount of charging of the batteryxe2x80x9d is interpreted to mean an amount of electric energy with which the battery is charged per unit time, namely, electric power W and the term xe2x80x9camount of electric energy presently stored in the batteryxe2x80x9d is interpreted to mean an amount of electric power Wh or Ah.
It is therefore an object of the present invention to provide a hybrid vehicle control apparatus which provides a further improvement in the fuel economy of an engine and which permits a hybrid vehicle to be driven with a drive force as desired by the vehicle operator even when the operator""s desired drive force is relatively large.
The above object may be achieved according to a first aspect of the present invention, which provides a control apparatus for controlling a hybrid automotive vehicle including an engine operable by combustion of a fuel and an electric motor as drive power sources for driving the vehicle, and an electric generator operable by the engine to generate an electric energy for charging a battery while the vehicle is driven by the engine, the control apparatus comprising a charging opportunity selecting device operable to determine whether the battery should be charged by the electric generator, on the basis of at least one of a required charging amount of electric energy with which the battery is charged and an energy conversion efficiency of the electric generator.
In the hybrid vehicle control apparatus constructed according to the first aspect of this invention, the charging opportunity selecting device is arranged to make a determination as to whether the battery should be charged by operation of the electric generator, on the basis of at least one of the required charging amount of the battery and the energy conversion efficiency of the electric generator. According to this arrangement, the battery is charged only when the energy conversion efficiency of the electric generator is relatively high, so that the fuel economy of the engine is accordingly improved. Further, the battery is charged when the speed of the engine is comparatively high, so that the charging does not take place when the accelerator pedal is released. If the battery charging took place upon releasing of the accelerator pedal, the engine speed Ne would be undesirably raised. Thus, the present arrangement prevents a rise of the engine speed due to the battery charging. Such rise and change of the engine speed upon charging of the battery is unexpected by the vehicle operator.
The required charging amount of the battery indicated above corresponds to an electric power generated by the electric generator, that is, the operating speed of the electric generator multiplied by the regenerative torque of the electric generator. Therefore, the energy conversion efficiency of the electric generator can be improved by permitting the charging of the battery only when the required charging amount of the battery is larger than a predetermined lower limit.
The control apparatus according to the first aspect of the invention is applicable to various hybrid automotive vehicles having a synthesizing/distributing device of a gear type such as a parallel or series type or a planetary gear type. The electric motor and the electric generator may be mutually separate units, or a single motor/generator unit which selectively functions as the electric motor or the electric generator. The present control apparatus is also applicable to a hybrid vehicle having a plurality of motor/generator units.
In one preferred form of the first aspect of the invention, the control apparatus further comprises means for determining the required charging amount of electric energy of the battery on the basis of an amount of electric energy presently stored in the battery. In this case, the electric generator is operated to charge the battery with the required charging amount. However, the electric generator may be operated to generate an electric energy so as to satisfy any other requirement relating to the charging of the battery. The electric generator may be mechanically connected to and driven by the engine. Alternatively, the electric generator may be driven by a rotary motion of the vehicle wheels transmitted thereto.
In a further preferred form of the control apparatus according to the first aspect of the invention, the charging opportunity selecting device determines whether the battery should be charged, on the basis of the energy conversion efficiency of the electric motor. In this case, the energy conversion efficiency of the electric motor need not be directly obtained. For instance, a permissible operating range (e.g., permissible operating speed and torque) of the electric generator within which the battery can be charged with a high energy conversion efficiency is determined, and the determination as to whether the battery should be charged is effected by determining whether the operating state of the electric generator is held within the permissible operating range.
In an alternative preferred form of the control apparatus, the charging opportunity selecting device determines whether the battery should be charged, on the basis of the required charging amount of the battery. Namely, the operating state of the electric generator is almost determined by the required charging amount of the battery as well as the vehicle-operator""s desired vehicle drive power. In this respect, the determination may be effected by determining whether a sum of the required charging amount of the battery and the operator""s desired vehicle drive power, which is the required total vehicle drive power, is larger than a predetermined threshold which is determined with the energy conversion efficiency of the electric motor being taken into account.
Other parameters such as the vehicle running speed, the operating amount of the accelerator pedal and the operating state of the brake pedal may be used to determine whether the battery should be charged or whether the charging of the battery should be permitted or inhibited.
When the vehicle operator requires the vehicle to be decelerated (for example, when the accelerator pedal is released or the brake pedal is operated) while the battery is charged by the electric generator, it is desirable to inhibit or interrupt the charging of the battery and turn off the engine. In this instance, the electric generator is operated by a kinetic energy of the vehicle, so as to generate an electric energy for charging the battery and a regenerative brake to be applied to the vehicle.
The control apparatus according to the first aspect of the invention is suitably applicable to the hybrid automotive vehicle which includes (a) a motor/generator which selectively functions as the electric motor and the electric generator, (b) an output member operatively connected to a drive wheel of the vehicle for driving the vehicle, (c) a synthesizing/distributing device of gear type connected to the engine, the motor/generator and the output member, for synthesizing and distributing forces among the engine, the motor/generator and the output member, and (d) a continuously variable transmission disposed between the output member and the drive wheel.
In the hybrid vehicle described above, the synthesizing/distributing device may include a housing, a first rotary element connected to the engine, a second rotary element connected to the motor/generator and connected to the output member through a first clutch, and a third rotary element connected to the output member through a second clutch and fixed to the housing through a brake.
The object indicated above may also be achieved according to the second aspect of this invention, which provides a control apparatus for controlling a hybrid automotive vehicle including an engine operable by combustion of a fuel and an electric motor as drive power sources for driving the vehicle, a continuously variable transmission through which at least a drive force generated by the engine is transmitted to drive the wheels of the vehicle, and an electric generator operable by the engine to generate an electric energy for charging a battery while the vehicle is driven by the engine, the control apparatus comprising: (a) a first engine/transmission control device operable upon charging of the battery, to increase a torque of the engine while shifting down the continuously variable transmission so as to increase an operating speed of the engine; and (b) a second engine/transmission control device operable upon an increase in a vehicle-operator""s desired drive power for driving the vehicle, to increase the torque of the engine and shifting down the transmission so as to increase the operating speed of the engine, the second engine/transmission control device including engine-output increasing means for increasing the torque of the engine, the engine having a throttle valve, and the engine-output increasing means having a response higher than the throttle valve.
In the hybrid vehicle control apparatus constructed according to the second aspect of this invention, the continuously variable transmission is shifted down when the battery is charged so that the output of the engine is increased, for example, along a first engine operating line which is formulated for improved fuel economy of the engine, as described below. Accordingly, the battery can be charged with a high degree of fuel consumption efficiency or fuel economy, without reducing the vehicle drive force. When the vehicle-operator""s desired vehicle drive power is increased, on the other hand, the torque of the engine is increased by the engine-output increasing means, and the continuously variable transmission is shifted down so that the operating speed of the engine is increased, for example, along a second engine operating line which represents a higher torque of the engine than the first engine operating line, as described below. Accordingly, the vehicle drive torque can be rapidly increased to a value large enough to drive the vehicle with high drivability.
The engine-output increasing means of the second engine/transmission control device, which has a higher response than the throttle valve, may include a variable valve timing mechanism (VVT), a D4 xlean-burn control device, an engine-power increasing device, a turbocharger or other suitable engine-power increasing device. If necessary, the electric motor may be operated to provide an assisting torque to be added to the engine torque, for assisting the engine to drive the vehicle, so that the acceleration response of the vehicle can be improved.
In one preferred form of the control apparatus according to the second aspect of the invention, the first engine/transmission control device controls the engine such that the operating state of the engine changes along a first engine operating line which is formulated for improved fuel economy of the engine, and the second engine/transmission control device controls the engine such that the operating state of the engine changes along a second engine operating line which is formulated to provide a larger torque than the first engine operating line, the first and second engine operating lines being defined by the torque and speed of the engine.
The second engine operating line indicated above may be a predetermined single line, or a selected one of a plurality of operating lines which is selected according to the vehicle-operator""s desired vehicle drive power or other parameter.
In another preferred form of the control apparatus according to the second aspect of this invention, the first engine/transmission control device shifts down the continuously variable transmission at a speed which is lower than that at which the continuously variable transmission is shifted down while the battery is not charged.
In the above form of the invention, the speed at which the continuously variable transmission is shifted down under the control of the second engine/transmission control device is lower than the speed at which the transmission is shifted down while the battery is not charged. This arrangement is effective to reduce an amount of variation in the vehicle drive force due to an inertia of the engine when the engine speed is increased as a result of a shift-down action of the transmission. Accordingly, the operating state of the engine can be changed following the first engine operating line indicated above, with high accuracy, so that the fuel economy of the engine can be further improved.
The shift-down speed of the continuously variable transmission can be reduced by smoothing the desired value of its input shaft speed, or by gradually changing the charging amount of the battery at a rate lower than a predetermined upper limit.
The control apparatus according to the second aspect of the invention is suitably applicable to the hybrid vehicle which includes (a) a motor/generator which selectively functions as the electric motor and the electric generator, (b) an output member operatively connected through the continuously variable transmission to a drive wheel of the vehicle for driving the vehicle, and (c) a synthesizing/distributing device of gear type connected to the engine, the motor/generator and the output member, for synthesizing and distributing forces among the engine, the motor/generator and the output member.
In the hybrid vehicle described above, the synthesizing/distributing device may include a housing, a first rotary element connected to the engine, a second rotary element connected to the motor/generator and connected to the output member through a first clutch, and a third rotary element connected to the output member through a second clutch and fixed to the housing through a brake.